As antenna switches used for mobile phones, in order to fulfill the multi-mode, multi-band demands, pHEMT switches using GaAs have been used from the viewpoint of linearity and strain suppression. However, GaAs platforms have a drawback in that power consumption cannot be decreased because of current leakage to substrates, and the like. Furthermore, a switching device needs to separately have decoder circuits made of Si provided outside thereof. Therefore, when a GaAs platform is used, it is not possible to integrate the circuits. Consequently, there is a limit to the reduction in size and cost.
In recent years, in order to solve the problem described above, there has been provided a SOI (Silicon on Insulator) technique (for example, refer to Patent Literature 1). A SOI wafer is known in which a SiO2 layer is formed on the upper portion of a Si layer, and another Si layer is bonded thereon as a functional layer. Furthermore, a SOI wafer is known in which an alumina substrate and a silicon substrate are bonded to each other (for example, Patent Literature 2).